Silicon valve

ABSTRACT

A silicon valve for controlling the flow of a fluid includes two generally planar silicon members. One has an orifice for passing the fluid and the other has a relatively moveable surface to selectively open and close the orifice thereby controlling the flow of fluid through the orifice.

TECHNICAL FIELD

This invention relates to a structure and method for chemically etchingand fabricating a silicon valve structure.

BACKGROUND ART

An article entitled "Fabrication of Novel Three-DimensionalMicrostructures by the Anisotropic Etching of (100) and (110) Silicon",by E. Bassous, IEEE Transactions on Electron Devices, Vol.. ED-25, No.10, October 1978, pages 1178-85 teaches the use of anisotropic etchingof single crystal silicon to make ink jet nozzles, optical waveguides,multisocket miniature electrical connector and electromechanicaldevices.

U.S. Pat. No. 4,157,935 issued to Solyst and U.S. Pat. No. 4,455,192issued to Tamai teach methods of forming an ink jet nozzle array bychemical etching of a silicon wafer.

It is also known to fabricate conventional metal fluid metering valvessuch as those using matched fittings of very precisely machined metalcomponents. Typical tolerances of the lapped machine parts are in themillionths of inches. This is a complicated, labor-intensive,time-consuming manufacturing process yielding components which areexpensive and subject to reliability problems as the internal toleranceschange due to wear and exposure to fuel and fuel contaminants. It wouldbe desirable to fabricate fuel injectors and other valves withsubstantially less labor and time using a significantly less complicatedmanufacturing process. That is, superior tolerances are desirable as isan insensitivity to fuel contaminants and improved reliability. Theseare some of the problems this invention overcomes.

DISCLOSURE OF THE INVENTION

This invention teaches a silicon valve for controlling the flow of fluidusing first and second silicon members. The first silicon member isgenerally planar and has an orifice for passing the fluid. The secondsilicon member has a planar silicon surface aligned with, and relativelymovable to, the orifice for selectively opening and closing the orificethereby controlling flow of fluid through the orifice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a movable silicon valve member in accordancewith an embodiment of this invention;

FIG. 2 is a side view of FIG. 1;

FIG. 3 is a plan view of a silicon valve member including a nozzleorifice for use in connection with the member of FIG. 1 in accordancewith an embodiment of this invention;

FIG. 4 is a section along section line IV--IV of FIG. 3;

FIG. 5 is a perspective view of the member of FIG. 1;

FIG. 6 is an alternative embodiment of the member of FIG. 1 using acircular instead of a square shape;

FIG. 7 is an alternative embodiment of the valve member of FIG. 3 usingfour nozzle openings instead of one opening;

FIG. 7A is an enlarged view of a portion of a plan view of the member ofFIG. 7 including a nozzle orifice which is etched obliquely through themember with respect to the planar surface of the member;

FIG. 8 is an exploded perspective view of two members of a silicon valveincluding a bottom valve member as shown in FIG. 7, and a top siliconvalve member in accordance with another embodiment of this inventionhaving an opening for passing a plunger to deflect the bottom siliconvalve member;

FIG. 9 is a bottom perspective view of the top valve member of FIG. 8;

FIG. 9A is a cross section view of the bottom valve member of FIG. 8along section line 9A--9A;

FIG. 10 is a bottom perspective view of a top valve member in accordancewith another embodiment of this invention for use in conjunction withthe bottom plate of FIG. 8;

FIG. 11 is an exploded perspective, partly cut-away view of a fluidmetering valve using a silicon valve in accordance with an embodiment ofthis invention;

FIG. 11A is a side, partly section, view of a fuel injector inaccordance with an embodiment of this invention;

FIG. 12 is an enlarged section view of the valve portion of a fluidmetering valve using the valve shown in FIG. 8 with a plunger passingthrough the central opening in the top silicon valve member and showinga fluid path by arrows to the sealed nozzle openings in the bottomsilicon valve member;

FIG. 12A is a view similar to FIG. 12 with the plunger depressed and thebottom silicon valve member deflected opening up a fluid path throughthe nozzle openings in the bottom silicon member as indicated by arrows;

FIG. 13 is a bottom perspective view, similar to FIG. 5, of a topsilicon valve member in accordance with another embodiment of thisinvention;

FIG. 14 is the top perspective view of a bottom valve member including anozzle orifice for use in cooperation with the top silicon valve memberof FIG. 13;

FIG. 15 is a cross section view of a silicon valve using the membersshown in FIGS. 13 and 14 assembled in a fuel injector showing fluid pathby arrows;

FIG. 15A shows the valve structure of FIG. 15 in a deflected positionpermitting fluid to pass through the bottom silicon member as indicatedby arrows showing fluid flow; and

FIG. 16 shows a perspective, partly broken away, view of the siliconvalve members of FIG. 15.

BEST MODE FOR CARRYING OUT THE INVENTION

A silicon valve includes a planar, upper silicon valve member 11 havinga raised central mesa 12, a sectional wall perimeter 13, and a flexiblemembrane 17 intermediate central mesa 12 and wall perimeter 13. Fourpassages 16 are located between sections of wall perimeter 13 to permitfluid flow across wall perimeter 13, (see FIGS. 1 and 2). The siliconvalve also includes a generally planar lower silicon wafer 14 having anozzle orifice 15 aligned with mesa 12 (see FIGS. 3 and 4). The siliconvalve operates by positioning silicon members 11 and 14 adjacent eachother so that mesa 12 covers nozzle orifice 15. When member 11 isdeflected and mesa 12 is spaced from opening 15, fluid can flow in fromthe side through passages 16 between the portions of wall perimeter 13and out through nozzle orifice 15. FIG. 16 provides an assembled,perspective, partly broken away view in accordance with anotherembodiment of this invention wherein the passages for permitting fluidflow across the perimeter wall are located in the lower silicon valvemember. Silicon members 11 and 14 are each formed by etching fromgenerally planar silicon wafers advantageously having a planar opticalsurface. The raised wall perimeter 13 around the edge of silicon member11 can have an additional passage opening for increasing the flow offluid between silicon members 11 and 14 to orifice 15. If desired, thethickness of silicon member 11 adjacent passage 16 can be thicker thanat membrane 17 to provide structural reinforcement

Referring to FIG. 6, a silicon member 66 has a generally circular shapewith a raised central circular mesa 62, generally arcuate sectionsforming a sectional wall perimeter 63 with radial passages 66, and anannular membrane 67 between mesa 62 and wall perimeter 63.

Referring to FIG. 7, an alternative embodiment of the lower siliconmember 14 can be a silicon member 71 having four nozzle orifices 72which are adapted to be aligned with either a large single or aplurality of smaller mesas to selectively regulate the flow of fluid.Advantageously, each nozzle orifice 72 is formed in an oblique anglethrough silicon member 71 so that fluid flowing through nozzle orifices72 is given a swirl.

FIG. 7A shows an enlarged plan view of a nozzle orifice 72 with theangling shown in two directions. The angling provides a spray orswirling to the fluid as to exits nozzle 72 which is particularlydesirable when atomization of the fluid is important. This feature maybe used advantageously when injecting fuel into a combustion cylinder.Anisotropic etching of silicon is a particularly advantageous way offorming such angled nozzle openings. Silicon is a desirable material touse because it is resistant to attack by most fluids, exclusive ofstrong bases. Further, single crystal silicon for use as the flexiblevalve member is advantageous because there is no intrinsic fatiguemechanism.

FIG. 10 shows the bottom perspective view of a top member suitable foruse with bottom silicon member 71 of FIG. 7 wherein a silicon member 100has four central mesas 101 which are aligned with and are sufficientlylarge enough to cover nozzle orifices 72 of silicon member 71.

Referring to FIG. 8, a silicon valve 80 includes an upper silicon member81 having a raised central mesa 82 with an opening 83 therethrough.Silicon member 81 further includes four corner wall-like perimeterportions 84 with intermediate passages 85 for passing fluid. Passages 85extend up to mesa 82. A lower silicon member 90 has four nozzle orifices91 aligned to be covered by raised mesa 82. Valve 80 operates as shownin FIGS. 12 and 12A by having a plunger 120 extend through opening 83 inupper silicon member 81 to push against a central portion of lowersilicon member 90 thereby uncovering nozzle orifices 91 from mesa 82 andpermitting fluid to flow through nozzle orifices 91.

Referring to FIG. 9A, a section view of lower silicon member 90 includesan annular trough 92 formed in the bottom of lower silicon member 90around nozzle orifices 91 so as to form a membrane 93 of reducedthickness. This permits the central portion of silicon member 90 withnozzles 91 to be deflected when plunger 120 presses down on the centralportion of silicon member 90.

Referring to FIG. 12, when valve 80 is mounted in a fuel injector 121 afluid flow path 122 is aligned with passage 85 of upper silicon member81 so that the fluid path reaches central mesa 82. However, when lowersilicon member 90 is undeflected, central mesa 82 covers nozzle orifices91 and stops fluid flow from continuing to a passage 123 below thecentral portion of lower silicon member 90.

Referring to FIG. 12A, plunger 120 has moved downward so as to deflectthe central portion of lower silicon member 90 thereby permitting fuelto flow through nozzles 91 into lower passage 123.

The plunger 120 shown in FIGS. 12 and 12A can be of a piezoelectricmaterial which expands in response to the application of electriccurrent. Thus, the length of plunger 120 increases and causes it todownwardly deflect central portion of lower silicon member 90.

FIGS. 12 and 12A also illustrate an optional additional fluid flowpassage 129 through the thickness of upper silicon member 81 which canpass fluid and is in communication with nozzles 91 when lower siliconmember 90 is deflected downward.

Referring to FIGS. 11 and llA, there is shown an exploded and anassembled view of a fuel injector, respectively, in accordance with anembodiment of this invention. The silicon valve 130 can use members suchas upper silicon member 11 and lower silicon member 14 as shown in FIGS.1 and 3, respectively. The injector has injector body portions 131, 132and 133 for providing a central fuel path and supporting valve 130.Member 132 has a central fuel path 134 which passes fuel to sideopenings 135 and into side radial openings 136. A generally square seat137 receives the bottom of lower silicon member 14. A generally circularseat 141 receives a circular piezoelectric bimorphous wafer element 140which is attached to upper member 11 and can deflect upper member 11.Passages 16 of upper silicon member 11 are aligned to receive fuel fromradial openings 136. A spring 137 keeps mesa 12 abutted against nozzle15 to prevent fuel flow. A return spring 138 applies a downward force topiezoelectric element 140. On actuation of the injector of FIG. 11, thespring force is overcome by application of electrical energy topiezoelectric bimorphous wafer element 140 which causes upwarddeflection of the central portion of upper silicon member 11 and clearsmesa 12 from nozzle 15 thereby permitting fuel flow. Return spring 137applied to the piezoelectric member causes the flexible member to closewhen the electrical energy is removed. FIG. 11A shows an assembled viewsubstantially similar to FIG. 11.

An alternative embodiment of valve 130 using wafers similar to uppersilicon wafer 11 and lower silicon wafer 14 is shown in FIGS. 15 and15A. The upper member of a valve 150, shown in FIG. 13, has an uppersilicon member 151 having a wall-like continuous perimeter 152, a raisedcentral mesa 153 and a thinner membrane 154 intermediate raised centralmesa 153 and perimeter 152.

Referring to FIG. 14, the top respective view of a bottom silicon member160 to be used in conjunction with upper silicon member 152 is shown. Acentral nozzle orifice 161 is formed through lower silicon member 160.Side fluid flow channels 162 are formed in each of the four sides oflower silicon member 160 so that there is a reduced thickness of siliconmember 160. As can be seen in FIG. 15, the extent of fluid channel 162toward nozzle orifice 161 is greater than the width of perimeter wall152 so that fluid can pass through channel 162 adjacent membrane 154 upto central mesa 153. An assembled view of the elements of FIGS. 13 and14 is shown in FIG. 16. This view and others show the valve platessubstantially thicker than actual for clarity.

Referring to FIG. 15, the valve does not permit fluid flow throughnozzle orifice 161 when mesa 153 closes it off. A piezoelectricdiaphragm 165 is attached to upper silicon member 152 by a siliconattachment 166. FIG. 15A shows activation of piezoelectric diaphragm 165which causes upper silicon member 152 to deflect thereby raising mesa153 from nozzle orifice 161 of lower silicon member 160. This permitsfluid flow through channel 162, adjacent membrane 154 and through nozzleorifice 161.

A typical fabrication sequence for manufacture of a silicon valve, suchas that shown in FIG. 16, is as follows:

Top plate fabrication (including a mesa seat and a reduced thicknessdiaphragm) includes the steps of cleaning half wafers (2" wafers cut inhalf), growing an oxide of 1 micrometer thickness, stripping thebackside oxide from the wafers, depositing boron to define a diaphragm,removing boron-silicate glass (BSG), growing oxide (at least 2000A),defining a valve seat pattern in oxide, etching the wafer in EDP (ananisotropic etchant), and etching the remaining SiO₂ in buffered HF forabout 5 minutes.

Bottom plate fabrication (i.e. the orifice plate) includes cleaning awafer, growing an oxide (at least 2000A), forming an oxide pattern onthe top side to define the orifices, etching the wafer in EDP, cleaningthe wafers, growing an oxide, forming a backside oxide pattern for anorifice and plate size, etching the wafer in EDP, and removing theremaining SiO₂ with BHF.

When both top and bottom plates are complete, they are bonded togetherto form the valve so that a wall portion of the top silicon member iscoupled to the surface of the bottom silicon member and a surface of thetop silicon member is relatively moveable with respect to the orifice inthe bottom silicon member for sealing the orifice to stop the passage offluid and for being spaced from the orifice for permitting the passageof fluid through the orifice.

Various modifications and variations will no doubt occur to thoseskilled in the various arts to which this invention pertains. Forexample, the particular size and shape of the mesa, raised perimeterand/or the orifice may be varied from that disclosed herein. Also, thesize and shape of the silicon members (round, square, triangular, etc..)may be varied from that disclosed herein. These and all other variationswhich basically rely on the teachings through which this disclosure hasadvanced the art are properly considered within the scope of thisinvention.

We claim:
 1. A silicon valve for controlling the flow of a fluidincluding:a first generally rigid planar silicon member having anorifice for passing the fluid; and a second silicon member having arigid planar silicon surface aligned with and relatively moveable tosaid orifice for selectively opening and closing said orifice therebycontrolling the flow of fluid through said orifice, said second siliconmember including: a thicker mesa means having a flat top for sealingsaid orifice; a raised perimeter portion means for coupling to saidfirst silicon member; membrane portion means peripheral to said mesameans for providing said second silicon member with increasedflexibility so that said mesa means can be positioned to seal saidorifice to stop fluid flow and can move away from said orifice to permitthe passage of fluid through said orifice; and a fluid passage means insaid perimeter portion means for permitting the passage of fluid pastsaid perimeter portion means.